Known walk-behind working machines include handles carrying throttle levers for regulating throttles, first clutch levers for operating first clutches to connect or disconnect the drive between engines and working members, and second clutch levers for operating second clutches to connect or disconnect the drive between the engines and traveling members. These three types of the levers are individually operated.
Such working machines unavoidably make loud noise and consume more fuel than is needed, even in case the working machines stop traveling, because the engines keep running at the same speed as the engines running when the working machines perform works.
To address this problem, one may propose a walk-behind working machine, as disclosed in JP-A-3-25033, arranged so that a clutch lever can be handled to operate a throttle lever as well as to engage or disengage a clutch for connecting or disconnecting the drive between an engine and traveling units.
FIG. 11 shows a throttle lever and a clutch lever of the working machine disclosed in JP-A-3-25033. The throttle lever designated at 202 and the clutch lever designated at 203 are pivotably mounted to a handle 201. To the handle 201, there is provided a linkage 204 connected to the clutch lever 203 and the throttle lever 202 for turning the throttle lever 202 upon pivotal movement of the clutch lever 203.
The linkage 204 includes a sector gear 206 formed integrally with a shaft 205 supporting thereon the throttle lever 202, a sector gear 208 formed integrally with a shaft 207 supporting thereon the clutch lever 203, an extension spring 209 connected at one end to the sector gear 206 and at the opposite end to the sector gear 208 for urging the sector gears 206, 208 into meshing engagement with each other, and an extension spring 210 for urging the clutch lever 203 in such a direction as to disengage a clutch (not shown).
Upon releasing of the clutch lever 203 from an operator's hand (not shown), the clutch lever 203 under the force of the extension spring 210 is made pivot about the shaft 207 clockwise, as shown by an arrow R, to disengage a clutch to stop propulsion of the working machine. The sector gear 208 also pivots clockwise together with the clutch lever 203, causing the sector gear 206 to pivot about the shaft 205 counterclockwise.
Upon the counterclockwise pivotal movement of the sector gear 206, the throttle lever 202 automatically pivots forward, as shown by an arrow, to a forward inclined position providing a reduced speed of the engine whist the extension spring 209 is shifted to a lower level than the shafts 205, 207. The shifted extension spring 209 urges each of the sector gears 206, 208 in such a manner to hold the throttle lever 202 in the forward inclined position.
By virtue of the thus arranged linkage 204, the clutch lever 203 can be operated to stop the propulsion of the working machine while operating the throttle lever 202 to reduce the speed of the engine so as to prevent production of loud noise and excessive consumption of fuel.
However, the linkage 204 can apply only to the machine including one throttle lever and one clutch lever. Namely, this linkage 204 is not applicable to such a walk-behind working machine as a self-propelled lawn mower designed so that, in addition to a throttle lever, a handle carries two clutch levers, one for operating a clutch to enable or stop rotation of cutting blades and the other for operating a clutch to enable or stop propulsion of the working machine. In the case of this type of the lawn mower, whenever each of the two clutches is engaged, the throttle lever should be operated to move a throttle from an opened position providing an idling speed of an engine to a further opened position providing a speed of the engine for rotating the cutting blades or propelling the lawn mower. It is preferable to provide the lawn mower with a linkage for controlling the throttle lever upon operation of a selected one of the two clutch levers.
What is needed is a technique useful for a walk-behind working machine including the above two clutch levers, as well as for a walk-behind working machine including either one of the two clutch levers. More specifically, such a conventional linkage as disclosed in JP-A-3-25033 needs to be improved to control a throttle lever upon operation of selected one of two clutch levers.